In 2006, the U.S. Environmental Protection Agency commissioned the Universal Technical Institute in Avondale, Ariz. to conduct tests to determine the amount of refrigerant remaining in do-it-yourself (DIY) small cans and professional 30 pound cylinders used to charge motor vehicle air conditioning (MVAC) systems. See, “Disposable Container Heel Testing Study Report”, Prepared for: United States Environmental Protection Agency Stratospheric Protection Division, Task Order No. 11, Contract No. EP-W-06-010 (Mar. 21, 2007), and peer review report, each of which is expressly incorporated herein by reference.
Under typical situations, any refrigerant remaining in disposable containers after charging a MVAC system is ultimately eventually released to the atmosphere. The releases are referred to as “heel emissions.” For small cans, the tests analyzed the heel remaining after various charging times under different scenarios. The tests of 30 pound cylinders quantified the heel remaining in cylinders that had been removed from service as “empty.”
Current MVAC systems use HFC-134a (1,1,1,2-Tetrafluoroethane) refrigerant. MVAC refrigerant emissions can come from leaks in the system, from servicing, and from end-of-life disposal. Servicing emissions can occur either at professional repair shops or through do-it-yourself (DIY) servicing. Repair shops generally use 30 pound cylinders and refrigerant recovery/recycling machines that minimize emissions. Do-it-yourselfers (DIYers) use small cans (typically 12 ounces) of refrigerant to recharge or top off an MVAC without the aid of certified service equipment.
Tests of 30 pound cylinder heels measured the amount of refrigerant remaining in the cylinder after a service shop had determined it was empty and had removed it from the charging equipment. The technicians conducted the tests at standard room temperatures. They weighed each cylinder before recovery of the cylinder contents, and measured and recorded the initial cylinder pressure. With the recovery/recycling machine, they performed two recovery cycles on each cylinder and measured the cylinder weights after each recovery cycle. The technicians pulled a vacuum (10 to 15 in. Hg) during the first recovery cycle. The recovery was completed after the pressure stabilized. They used a different procedure during the second recovery cycle to examine the effects of pulling a deeper vacuum (30 in. Hg). They also applied a heat blanket during the second recovery and oriented the cylinders upside down to transfer the refrigerant in the liquid phase.
The heel testing results for each of six 30 pound cylinders show that the average heel was 1.85%, with a range from 0.302 to 4.46%. This means that an average of 0.55 pounds, and a range of 0.09-1.39 pounds remain in the cylinder after exhaustion in the field.
Similar 30 pound cylinders are used in other industries, and various refrigerant gasses are transported in similar containers. However, the issue of residual gas remaining in the cylinder after use remains apparent in all such cases.
The cylinders are generally single use because reuse would require determination of contaminant status and DOT container certification status, possible inspection and retesting, and significant logistical overhead in returning the containers to refilling plants. On the other hand, non-reusable containers are “virgin”, and are efficiently manufactured from steel, tested, filled and distributed. Of course, the exhausted containers end up in landfills, eventually leaking their residual content.